Building A Linux Music Studio Part 2

Fixing Volume Levels

January 3, 2008

By
Carla Schroder

Last week we made a music CD from a live digital recording the easy and simple way. Today we're going to fix volume levels and do graceful fades and transitions using Audacity and normalize. Give yourself a lot of disk space, make copies of your original sound files before you start, and remember that Audacity has Undo and Redo commands, so don't stress out over making mistakes.

Normalization is a term you hear a lot, and it has two different meanings. One is to adjust all tracks to the same volume level, so that you're not surprised by a loud song following a soft song. Another meaning is to amplify a single track proportionally, or part of a track, making it as loud as possible while preserving its dynamic range. Audacity does the latter, but it cannot normalize a diverse batch of songs. For that we use the excellent command-line tool, normalize.

First let's see what Audacity can do. Select the track or portion of track that you want to normalize, then hit Effect--Normalize. For now stick with the default settings, which is to have "Remove any DC offset" checked, and "Normalize maximum amplitude to -0.0 dB". Figure 1 shows a track with three songs that were recorded at too low a level. We have two options here: normalize the entire track, or portions of it. Figure 2 shows what happens when the whole track is normalized at once. The first song is still a lot quieter than the second song. So I can select the first song and normalize it, as Figure 3 shows. Now it's about the same volume level as the second song.

Use the Amplify command for more control over volume levels. Highlight the part you want to change, go to Effect--Amplify, and set your desired level, either higher or lower.